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Experimental Conditions and Techniques in Carbenoid Chemistry

Most lithium halocarbenoids decompose at temperatures above — 80 to — 90 °C. An essential condition for a successful synthesis via a (preformed) lithium halocarbenoid is that its generation proceeds at a high rate at temperatures below this range. For this reason, the more polar THF is preferred to Et20 as a main solvent for the deprotonation or lithium-halogen exchange reactions by which the carbenoids are formed. [Pg.175]

Because of the increase of the viscosity of THF at very low temperatures, stirring becomes less efficient. For this reason, Et20 and/or a low-boiling petroleum ether fraction are used as co-solvent. Especially in reactions that have to be carried out below — 110°C, relatively large amounts of solvents are necessary, which puts limitations on the scale of the synthesis (usually not higher than 50 mmol at these very low temperatures, unless adapted equipment is available). [Pg.175]

For general instructions concerning handling organolithium reagents, drying solvents, etc., see Vol. 1. [Pg.175]


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